Methods of making partially hydrolyzed fucoidan. Fucoidan from brown seaweeds is partially hydrolyzed and then mixed with other ingredients for use as a dietary supplement in beverage, capsule, or tablet form. The fucoidan is partially hydrolyzed with acid and heat. The partially hydrolyzed fucoidan can also be sulfonated. Other ingredients that can be included in the dietary supplement include high-ORAC-value antioxidants, minerals, pepper extract, flavoring agents, coloring agents, and preservatives. The compositions can be in the form of beverages, tablets, capsules, powders, and the like.